The technique is maggot debridement therapy. Eggs are surface-sterilised, the hatched larvae are applied to a wound under a dressing, and they remove necrotic tissue by secreting proteolytic enzymes and ingesting the liquefied result. Lucilia sericata is chosen because its larvae confine themselves to dead tissue, unlike the larvae of some other blowflies that invade living flesh.
The practice was recorded in military surgery long before it was regulated: wounds that had become infested in the field were repeatedly noted to be cleaner than expected. It fell out of use with antibiotics and returned as antibiotic-resistant infections became harder to treat.
The same species matters in forensic entomology. Blowflies are among the first insects to reach a body, and because larval development rate is a known function of temperature, the size and stage of the larvae present supports an estimate of the minimum time since death.